Comment by Olivier Paillard (JIRA)

I just encountered the same bug with the latest version of Swift/Xcode (Swift 4.1 with Xcode 9.3) released last week.

(all was fine with Swift 4.0 / Xcode 9.2)

@phausler @natecook1000 any idea on this?

26.7 does not convert to Float losslessly so it fails the litmus of the cast of being able to be represented “safely”. This is similar to the concept of Int64.max not being able to be represented as Int32

So this behaviour changed on purpose from Swift 4.0 to Swift 4.1? Is this anywhere noted?

Comment by Mark Sands (JIRA)

This is really unexpected and has caused a lot of subtle bugs. It would have been nice to more clearly communicate this in release notes. This legacy code works in Xcode 9.3 but silently fails in Xcode 9.4:

let jsonDict: [String: Any] = ["price": 2.18]

let data = try! JSONSerialization.data(withJSONObject: jsonDict, options: [])

let json = try! JSONSerialization.jsonObject(with: data, options: []) as! [String: Any]

json["price"] as? Float? // 2.18 or nil depending on the version of Swift

Comment by Mark Sands (JIRA)

(lldb) po type(of: json[“price”])

__NSCFNumber

Comment by Olivier Paillard (JIRA)

Actually I realized this problem using `JSONSerialization` too.

Surprisingly by using `Codable` protocol for my objects and `JSON[En,De]coder` instead of `JSONSerialization`, it solved my issue (about conversion to `Float`).

I deduce that the casting is not implemented the same way in the `JSONDecoder` black box.

Comment by Philipp Weber (JIRA)

Also stumbled across this error a few days ago in our app, though in our case it only appears on 32bit devices, in our case the iPod touch 5th gen.

Our code is like this:

//json : [String Any]

quality.skillScore = json["skillScore"] as? CGFloat ?? 0.0

Values in this JSON lie between 0.0 and 1.0.

When a value of, let's say 0.975 is the value for skillScore, the above conditional cast fails on 32bit systems and the default of 0.0 is set for skillScore.

When checking for the type, Swift determines the type of json["skillScore"] to be a Double, which is correct. But since CGFloat's nativeType on 32bit is Float, the cast fails.

This code used to work in Swift 4.0.3, but seems to have regressed in 4.1

I will most likely remedy this by changing the type of quality.skillScore to be a Double and convert to CGFloat when needed for drawing code.